Not Just Motor Efficiency: Look at the Whole System

While Upgraded Components Can Boost Energy Efficiency, a System-Level Review Is More Likely to Pay Off Big

By Aaron Hand

ABB A&PW 2012

Ever-increasing electricity costs are a universal problem. As plants look for ways to mitigate those costs, energy efficiency is the simplest, least-expensive way to go. And yet nearly a quarter of the facilities (24%) have not addressed energy in any way, according to John Malinowski, senior product manager, ac motors, for Baldor Electric, and chairman of NEMA's motor and generator section. "They just assume it's a fixed cost, and there's nothing they can do about it," he said.

Particularly as more laws go into effect mandating improved efficiencies in motors, reviewing and updating the motors in a plant is a good first step in improving plant energy efficiency. An even better step, however, is doing a full review of system efficiency—looking beyond the motor at the application as well, adding adjustable-speed drives on pump and fan applications, using increased-efficiency gear reducers and premium-efficiency transformers, and adding servos for increased throughput. "Something like using servos will use more electricity, but your throughput will be higher," Malinowski explained. "So my electricity might go up, but at the end of the day, looking at kilowatt-hours per widget, my number goes down."

Malinowski explained the benefits of system efficiency during a session at ABB Automation & Power World 2012 this week in Houston. To explain the importance of considering a motor's efficiency level, he pointed out that energy accounts for more than 97% of a 20-year lifecycle cost of a motor. "About 2% is the purchase of the motor itself. The rest of it is cost of operation," he said. "Investing upfront in the motor is going to save a whole lot as time goes on."

On this point, purchasing agents need to be educated on the benefits of spending more for a high-efficiency motor. "Purchasing agents are there to save money when they buy things," Malinowski said. "So they're going to fight against spending money up-front, and they're going to hurt you on this."

Upgrading just one 200-hp, four-pole motor from average efficiency (93.5%) to NEMA premium efficiency (96.2%) could save a plant close to $80,000 over a 20-year period, not even considering the rising cost of energy during that time. According to Department of Energy (DoE) estimates, replacing lower-efficiency motors could translate to $3 billion to $5 billion in savings every year in the United States. Waiting until those motors fail to replace them could take 15 to 20 years.

But it's more than just upgrading to premium-efficiency motors. DoE best practices, as Malinowski pointed out, also encompass improving rewind practices, reducing system load, controlling motor speeds, matching equipment to the load, upgrading component efficiency, maintenance practices and motor downsizing (right sizing).

"When a motor fails, find out why it failed," Malinowski urged. "Work with the service shop and have it give you a good assessment." He told of one plant that replaced the same motor over and over again, until engineers finally discovered that they were using a motor that wasn't designed for the application. It was getting water in it and needed an upgraded enclosure.

A basic plant survey that anyone could do would involve inventorying motors and deciding what to do with them when they fail, Malinowski said. A more advanced survey would add measuring the current draw on each motor to determine appropriate sizing. A third level of plant survey is a full-system approach. "Put your engineer hat on, stand back and look at more of an expenditure level here," he said, explaining that the first two levels work more with existing motors, while the third level is more an overhaul.

It's not difficult to look at system-level efficiency—any number of organizations can perform assessments, or your own plant people can do the surveys—and the payback is significant. The Baldor Energy Savings Tool can provide a payback analysis that quickly brings to light the fact that switching out motors might take you 30 to 32 months to recoup the investment, while using a drive could shorten the payback period to more like six to eight months, Malinowski said.

"You've got to look at the systems," he said. "We can save money by replacing components, but it's minimal. A motor might give you 6% to 8%, but one of these system improvements might give you 50% to 60%. Electricity costs are going to keep going up, so you'll save more if you do it now."